Re: [PATCH] KVM: x86: fix xen guest panic due to lack of KVM_REQ_EVENT

From: Wanpeng Li
Date: Mon Aug 25 2014 - 05:38:43 EST

Hi Paolo,
On Mon, Aug 25, 2014 at 11:16:16AM +0200, Paolo Bonzini wrote:
>Il 25/08/2014 11:08, Wanpeng Li ha scritto:
>> Hi Paolo,
>> On Mon, Aug 25, 2014 at 11:01:07AM +0200, Paolo Bonzini wrote:
>>> Il 25/08/2014 09:58, Wanpeng Li ha scritto:
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index c10408e..b7c0073 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -4928,6 +4928,8 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
>>>> if (!mask)
>>>> kvm_make_request(KVM_REQ_EVENT, vcpu);
>>>> }
>>>> + if (!(int_shadow || mask))
>>>> + kvm_make_request(KVM_REQ_EVENT, vcpu);
>>>> }
>>>> static void inject_emulated_exception(struct kvm_vcpu *vcpu)
>>> No, this patch undoes the optimization in the buggy patch.
>>> A KVM_REQ_EVENT must be missing somewhere else.
>> Could you give some tips in order that I can figure it out?
>I have no idea right now (I was planning to debug it this week).
>(BTW, look at the original commit that introduced KVM_REQ_EVENT --
> -- and
>compare the patch and the commit message. You can see that it was added
>to the emulator because it is a "place that can set EFLAGS" and this
>idea is preserved in the buggy patch).
>The important thing is that (despite Xen being involved) this is not
>related to nested virtualization. So I would first of all try to see if
>some module parameter makes it go away (apicv and unrestricted mode

This bug can be reproduced w/o apicv.

>especially), then capture a trace of the panic. At least this is how I
>was planning to start... :)

Great, I will also continue to debug it. ;-)

Wanpeng Li

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